PHYLOGENY AND BIOGEOGRAPHY OF THE ATLANTIC AND EASTERN PACIFIC HYPSELODORIS STIMPSON, 1855 (NUDIBRANCHIA, CHROMODORIDIDAE) WITH THE DESCRIPTION OF A NEW SPECIES FROM THE CARIBBEAN SEA

Abstract

A new species, based on two specimens from Guana Island, British Virgin Islands, is described. The new species agrees with the genus Hypselodoris in having a high body profile, a large vestibular gland and mantle glands. It differs from other members of the genus in the Atlantic Ocean by having a reddish background body colour. In addition, dorsal colour patterns such as a broad central white line with lateral extensions and the lack of yellow lines or spots further differentiate this species. The radular formula of 52 x 41.0.41 and a smaller seminal receptacle are also distinctive. The phylogenetic relationships of 34 species and subspecies of Hypselodoris from the eastern Pacific and Atlantic are examined using morphological characters. With the exception of the new species, these are characterized by a dark blue background body colour. The phylogenetic analysis of the data matrix resulted in eight most-parsimonious trees. The resulting consensus tree shows that eastern Pacific and Atlantic species of Hypselodoris constitute a monophyletic group that is basally split into two sister clades. One clade contains the eastern Pacific species and most of the Caribbean species, whereas the other clade contains the eastern Atlantic species. The new species is the sister to the rest of the Caribbean species, which also form a monophyletic group. This phylogenetic hypothesis suggests that two consecutive vicariant events have affected the biogeography of Hypselodoris: (1) the closure of communication between the tropical Indo-Pacific region and the Atlantic and eastern Pacific, completed with the formation of the East Pacific Barrier; and (2) the rise of the Panama isthmus.